Estimation of surface structure and carbon monoxide oxidation site of shape-controlled Pt nanoparticles.

Surface structures of shape-controlled Pt nanoparticles have been estimated using cyclic voltammetry (CV) and infrared reflection absorption spectroscopy (IRAS). Cubic and cuboctahedral Pt nanoparticles are prepared using a capping polymer. These nanoparticles give CVs similar to those of single crystal electrodes of Pt in sulfuric acid solution. The CV of cubic nanoparticles is similar to that of the Pt(510) [=5(100)-(110)] electrode, while the CV of cuboctahedral nanoparticles is reproduced well with the convolution of Pt(766) [=13(111)-(100)] and Pt(17 1 1) [=9(100)-(111)] electrodes. These results suggest that the planes of the cubic and cuboctahedral nanoparticles are composed of step-terrace and atomically flat terraces, respectively. Adsorbed carbon monoxide (CO) on the shape-controlled nanoparticles gives the IR bands that are assigned to on-top and bridged CO. The band of on-top CO is deconvoluted to two bands: the higher and the lower frequency bands are assigned to the CO on the plane and the edges of the nanoparticles, respectively. On-top CO adsorbed on the edges is oxidized at more negative potential than that on the planes. Edge sites of the nanoparticles promote CO oxidation.